Method of forming a lubricating element by electrophoresis



2,994,654 METHOD OF FORMING A LUBRICATIN G ELE- MENT BY ELECTROPHORESIS Frederick Fahnoe, Morristown, and James J. Shyne,

Caldwell, NJ., assignors to Vitro Corporation of America, New York, N.Y.

No Drawing. Filed Feb. 4, 1958, Ser. No. 713,083 4 Claims. (Cl. 204-181) Our invention relates to lubricating elements and methods for producing the same.

The generic term lubricating element applies to such devices as bearings, bushings and other like articles wherein one member slidably engages another member or wherein two bodies in contact with each other are adapted to move relative to each other with ease. In order to prevent high friction, freeze-up, and other associated phenomena, the frictional coeflicient of any element ideally should be held constant and in particular should be substantially independent of temperature. As far as is known to us, known elements have frictional coefficients whose values change sharply with tempera ture. Typical operating temperatures for lubricating ele' ments have greatly increased over those used only a few years ago and an urgent demand has been created for lubricating elements whose frictional coefficients have improved thermal stability. Moreover, the element itself must be securely bonded to a supporting member and known bonds will rapidly disintegrate at these increased temperatures. Furthermore, the working surfaces of known elements will deteriorate rapidly and fail under the influence of the severe thermal stresses created by these temperatures.

Accordingly, it is an object of the present invention to provide improved lubricating elements which obviate these disadvantages.

It is another object to provide novel methods for producing these improved elements.

A further object is to provide improved lubricating elements with thermally stable frictional coeflicients.

Still a further object is to provide a novel method for electrophoretically forming lubricating elements.

Yet a further object is to provide a novel method for bonding lubricating elements to a supporting member.

Another object is to provide lubricating elements which exhibit good resistance to wear at high operating temperatures.

In our copending application Serial No. 388,119, filed October 26, 1953, now Patent No. 2,858,256, there are disclosed processes for depositing layers of finely divided material on a surface by electrophoresis. We have now discovered that the electrophoretic techniques disclosed therein can also be used in producing lubricating elements.

Electrophoretic deposition occurs when an electrostatic field is established between two electrodes immersed within a colloidal or gross dispersion of charged particles, thus causing the migration of the suspended particles toward one of the electrodes and producing the deposit of an adherent coating on that electrode. Exceptional uniformity of coating thickness and compacting (with an attendant relatively high coating density) are obtained as compared with dipping, spraying, brushing, and other more conventional methods of application. Irregularly shaped objects of any desired contour can be coated with excellent uniformity and reducibility of coating.

Further details of this process will be found in the above mentioned application.

In the present invention, a mixture comprising a major portion by weight of particles of a reducible metallic compound and a minor portion by weight of particles of suitable solid lubricant is electrophoretically codeposited on a base member of any desired shape and contour. The

atent coated member is then heated to a temperature less than the softening temperature of the compound, if necessary in a reducing atmosphere, to reduce the metallic compound to metal and form a metal matrix Whose interstices entrap the particles of the solid lubricant. The amounts of lubricant and matrix forming material are such that the layer after reduction contains -95% by weight of metallic matrix and l55% of lubricant. As the reduction takes place, co-difl'usion between the deposited metal and the base member occurs at their interface and a strong durable bond is formed.

For low or anti-friction elements adapted, for example, to withstand temperatures on the order of 500 F., the reducible compounds can be oxides of such refractory metals as nickel, copper, or alloys of these metals, but also can be oxides of tin, lead, silver or their alloys. The lubricant must have a low friction coeflicient and can be, for example, molybdenum disulfide, tungsten disulfide, graphite or the like.

The base member in this type of application is generally composed of various metals and alloys. Electrophoretic deposition can only occur satisfactorily when the receiving surface has an electrical conductivity at least equal to that of a semi-conductor. In the event that the base member to be used has a non-conductive receiving surface, this surface must first be treated to render it conductive be fore the deposition takes place, for example, by one of the methods disclosed in our copending application, Ser. No. 398,129, filed December 14, 1953, now abandoned.

The following examples set forth certain well-defined instances of the application of this invention. They are, however, not to be considered as limitations thereof, since many modifications may be made without departing from the spirit and scope of this invention.

Example 1 A mixture comprising about 86% by weight silver oxide particles, about 6% by weight of copper oxide particles and about 8% by weight of molybdenum disulfide particles was ball milled for a period of from 100 to 200 hours in 5% concentration in a medium of 50% by weight of glycerine and 50% by weight of isopropyl alcohol. The resulting dispersion was activated by continuous agitation for a period of about one hour.

This dispersion was then poured into a conventional electrophoretic bath. A steel sleeve 6" in length and having an internal diameter of 2" was suspended in the dispersion. A steel rod 6" in length and having a diameter of A" was suspended in the dispersion in such manner that the axis of the rod coincided with the axis of the sleeve. A direct voltage of 250 volts was applied between the sleeve and rod with such polarity that the sleeve functioned as the cathode. The silver oxide-copper oxide-molybdenum sulfide particles immediately began to deposit uniformly on the internal surface of the sleeve. After a 55 second interval, the sleeve was disconnected and removed from the bath. The deposited coating attained a thickness of microns during this interval.

The coated sleeve was then fired in hydrogen at a temperature of 1300 F. for a period of 15 seconds. The heating was carried out by placing the samples in the furnace at a much lower temperature, generally room temperature, starting the hydrogen stream, heating the furnace to temperature, maintaining the furnace temperature for the specified time, and then allowing the furnace to cool while maintaining the hydrogen atmosphere until the temperature was below that at which oxidation would occur. Subsequent cross-sectional analysis revealed that extent during the firing operation. The weight composition of the reduced coating was about 85% silver, 5% copper and molybdenum disulfide.

Tests; revealed that the 'coefiicient of friction for the sleevewas, on the order of .10. and exhibited. little variation asv the operating temperature was increased: from 70 to 500 F. As the temperature increased beyond this latter value, matrix began to soften and separate from the sleeve.

This. experiment was repeated with various percentages of molybdenum disulfide and it was found that best results. were obtained by maintaining the percentage by weight; of. molybdenum disulride between the limits of 5 to By repeating the deposition and firing process as many times as necessary, coating thicknesses up to 3000. microns and higher can be built up.

Example 2 Example 1 was repeated using an initial mixture of lead oxide, tin oxide, copper oxide and graphite particles. After electrophoretic deposition of the particles and subsequent firing at a temperature of 800 F. for a period of 30 seconds, a matrix of a lead-tin-copper alloy containing entrapped graphite within its pores was formed having a composition by weight of 78.4% lead, 9.0% tin, 2.6% copper and 10% graphite.

The coefficient of friction of this sleeve was found to be on the order of .1 over the same general range as Example 1. Increasing the percentage of graphite decreases the coefiicient of friction but also weakens the matrix. structure so that best results are obtained by maintaining the percentage by weight of graphite within the range 515%.

Although in the above examples, we have indicated certain definite firing temperatures, duration of reactions, types of materials, coefiicients of friction, etc., it is to be understood that any or all of these can be varied widely within the scope of our invention, since the particular conditions of operation are governed largely by the specific end structure desired. For example, the firing temperature must be high enough to perform the desired reduction and low enough to prevent softening or melting of the materials used. The actual temperature used will vary depending on the characteristics of these materials.

Therefore, it is apparent, that many widely different embodiments of this invention can be made without departing from the spirit and scope thereof and we do not intend to be limited except as indicated in the appended claims. This application is a continuation-in-part of our copending application Serial No. 402,402, filed January 5, 1954, now Patent No. 2,828,254.

We claim:

1. The method of forming a lubricating element which comprises the steps of electrophoretically depositing a particle mixture having a metallic matrix forming material of the group consisting of nickel oxide, copper oxide, silver oxide,, lead oxide, tin oxide, and a solid lubricant of the group consisting of molybdenum disnlfide, tungsten disulfide and graphite, out of a liquid medium upon a selected surface of a metallic base member, the amount of matrix forming material and solid lubricant producing a layer having -95% by weight of metallic matrix and 15-5% by weight of solid lubricant, and heating said member in a reducing atmosphere at a temperature to reduce said matrix. forming material to form a metallic matrix bonded to said member, the interstices of said matrix being filled with said solid lubricant, without reducing said solid lubricant.

2. The method of claim 1 wherein the matrix forming material is a mixture of silver oxide and copper oxide and the lubricant is molybdenum disulfide, and the member is heated in a hydrogen atmosphere to reduce the matrix forming material to metal.

3. The method of claim 1 wherein the matrix forming material is a mixture of lead oxide, tin oxide and copper oxide, the solid lubricant is graphite and the member is heated in a hydrogen atmosphere to reduce the matrix forming material to metal.

4. The method of claim 1, wherein the liquid medium is an organic liquid.

References Cited in the file of this patent UNITED STATES PATENTS 2,848,391 Fahnoe et al Aug. 19, 1958 2,861,935 Fahnoe et al Nov. 25, 1958 OTHER REFERENCES Roehl, in Metal Finishing, May 1944, pp. 313-315.

Shyne et al., in Plating, October 1955, pp. 1255- 1258. 

1. THE METHOD OF FORMING A LUBRICATING ELEMENT WHICH COMPRISES THE STEPS OF ELECTROPHORETICALLY DEPOSITING A PARTICLE MIXTURE HAVING A METALLIC MATRIX FORMING MATERIAL OF THE GROUP CONSISTING OF NICKEL OXIDE, COPPER OXIDE, SILVER OXIDE, LEAD OXIDE, TIN OXIDE, AND A SOLID LUBRICANT OF THE GROUP CONSISTING OF MOLYBDENUM DISULFIDE, TUNGSTEN DISULFIDE AND GRAPHITE, OUT OF A LIQUID MEDIUM UPON SELECTED SURFACE OF A METALLIC BASE MEMBER, THE AMOUNT OF MATRIX FORMING MATERIAL AND SOLID LUBRICANT PRODUCING A LAYER HAVING 85-95% BY WEIGHT OF METALLIC MATRIX AND 15-5% BY WEIGHT OF SOLID LUBRICANT, AND HEATING SAID MEMBER IN A REDUCING ATMOSPHERE AT A TEMPERATURE TO REDUCE SAID MATRIX FORMING MATERIAL TO FORM A METALLIC MATRIX BONDED TO SAID MEMBER, THE INTERSTICES OF SAID MATRIX BEING FILLED WITH SAID SOLID LUBRICANT, WITHOUT REDUCING SAID SOLID LUBRICANT. 